Transcranial Doppler

Ultrasound technique for measuring blood flow velocity in the brain

A transcranial Doppler ultrasound being performed.

Doppler ultrasound analyzer of blood velocity.

TCD Spectroscopy equipment.

Different paradigms in TCD spectroscopy.

Transcranial Doppler (TCD) is a non-invasive ultrasound technique used to measure the velocity of blood flow through the brain's blood vessels. It is primarily used to assess the cerebral circulation and diagnose conditions affecting blood flow to the brain.

History

The development of transcranial Doppler ultrasound began in the early 1980s. It was first introduced by Rune Aaslid, a Norwegian physicist, who demonstrated its potential for measuring blood flow velocity in the major cerebral arteries. Since then, TCD has become a valuable tool in both clinical and research settings.

Technique

Transcranial Doppler uses a handheld probe that emits ultrasound waves through the skull. These waves are reflected off moving red blood cells within the cerebral arteries, and the frequency shift (Doppler effect) is used to calculate blood flow velocity. The procedure is typically performed through the temporal bone, which is one of the thinnest parts of the skull, allowing for better ultrasound penetration.

Clinical Applications

TCD is used in various clinical scenarios, including:

• Detection of vasospasm: Following a subarachnoid hemorrhage, TCD can monitor for vasospasm, a condition where blood vessels constrict, potentially leading to ischemia.
• Assessment of cerebral autoregulation: TCD can evaluate the brain's ability to maintain stable blood flow despite changes in systemic blood pressure.
• Monitoring during carotid endarterectomy: TCD is used intraoperatively to monitor cerebral blood flow and detect emboli.
• Evaluation of sickle cell disease: In children with sickle cell disease, TCD is used to assess the risk of stroke by measuring blood flow velocity in the cerebral arteries.

Advantages and Limitations

TCD is advantageous because it is non-invasive, relatively inexpensive, and can be performed at the bedside. However, it has limitations, including operator dependency and difficulty in obtaining adequate signals in some patients due to thick skull bones or poor acoustic windows.

Related pages

• Doppler ultrasound
• Cerebral circulation
• Ultrasound imaging